Its a well known fact that the right brain (more or less) governs creativity, emotional processing and non-linearity whereas the left deals more with reason, logic and the passage of time. It also does imply that we use different sides more actively while engaging in different tasks. However every individual has a preference for using one particular side more than the other - thereby determining what one is good at. A simple 'pop-psychology' test would be in deciding which ear you would put onto a closed door if you wanted to listen to what is going on at the other end. Right ear implies left brain processing and the left ear would imply the right.

Then I began to wonder, could there be any other way to ascertain a preference? Thats when I decided to observe half-smiles or smirks as you might call them. Being mostly around left brained people, I realized that most of them always smirk with the right side of the lip going up (Yay! for me) and so I decided to observe an entirely different set of people - Actors. And no surprise there! About 80% of the smirks I see across TV Shows/Movies shows that actors prefer to smirk with the left side of their lip going up first. Acting, as you may have guessed is a predominantly right brained activity requiring a sense of empathy forcing some aount of 'merging' with the character to be portrayed - something the left brain would find almost impossible.

As an example of what I've been on about, below are pictures of Andrew Scott (who plays Jim Moriarty) and Benedict Cumberbatch (who play Sherlock Holmes) in Steven Moffat's Sherlock.

Andrew Scott has a distinct right-brainer smile..

.. while Benedict has the exact opposite..

If you do observe closely, their acting styles are completely different with Andrew taking on a raw approach (maybe his character demands it, so I might be wrong) whereas Benedict's is highly cerebral (watch him here as well as in Tinker Tailor Soldier Spy)